1. Field of the Invention
Embodiments of the present invention are directed to novel compounds comprising hybrid cubic/hexagonal diamondoids. More specifically, embodiments of the present invention are directed to four compounds, each of which exhibit both the cubic diamond structure and the hexagonal diamond structure.
2. State of the Art
There are two forms of the diamond crystal structure, one hexagonal, the other cubic. As discussed in Carbon Molecules and Materials, edited by R. Setton, P. Bernier, and S. Lefrant (Taylor and Francis Inc., London and New York, 2002), a new phase of carbon, the hexagonal phase, was found among the crystals of cubic diamond in an x-ray diffraction experiment of synthetic diamond carried out at pressures greater than 130 GPa. According to Setton et al., the hexagonal phase may be obtained from pyrocarbons that have been subjected to a compression perpendicular to the layers, followed by annealing at a temperature greater than 1300 K. Hexagonal diamond has the lattice cell parameters ahexagonal=2.52 Å=acubic/√2, =4.12 Å=2ccubic/√3, and a P63/mmc space group. The density of hexagonal diamond is 3.51 g/cm3, which is the same as that in cubical diamond, and the position of the carbons is the same as the atomic positions in the wurtzite crystal structure. A hexagonal diamond crystal cage is shown in FIG. 1A, where only the carbon atom lattice sites have been shown (at the line intersections), and the hydrogen atoms have been omitted.
Also discussed in Carbon Molecules and Materials are the properties of cubic diamond. Cubic diamond has a space group of Fd3m, with the latice cell parameters acubic=bcubic=ccubic=3.5597 angstroms. Cubic diamond has 8 atoms per unit cell, and a density of 3.51 g/cm3. The carbon atoms of cubic diamond are all in the chair conformation, as illustrated in FIG. 1B, where again, only the carbon atom lattice sites have been shown.
Cubic diamondoids are known in the art. What has not been disclosed are diamondoids that contain both the cubic and hexagonal forms of the diamond crystal structure. Each of the four hybrid cubic/hexagonal compounds of the present invention have the stoichiometric formula C26H32 and a molecular weight of 344.